I. Field of the Invention
This invention relates generally to electrosurgical apparatus, and more particularly to a monopolar polypectomy snare incorporating means for effecting coagulation at the site of the polyp removal.
II. Discussion of the Prior Art
Various electrosurgical devices are known in the art which can be routed through endoscope into the gastrointestinal tract for removing polyps from the walls of the tract. The Treat U.S. Pat. No. 4,493,320 describes a bipolar electrocautery surgical snare capable of performing the endoscopic removal of growths, such as polyps, within a body cavity. That device comprises an elongated flexible insulating double lumen tubular member through which a pair of insulated conductors pass the distal end segments of these two conductors and are stripped free of insulation and are joined together by a small insulating button, thus forming a bipolar pair. When a pedunculated polyp is lassoed by the snare and then the snare wires are retracted in the proximal direction to close the loop, a point is reached where the tissue comprising the stalk of the polyp bridges the gap between the two electrodes and is cut off. If properly manipulated, any bleeding is cauterized.
The Komiya U.S. Pat. No. 4,311,143 describes an alternative arrangement for a bipolar polypectomy snare in which the entire loop comprising the snare is at the same electrical potential and a bipolar mating electrode is affixed to the distal end of the tubular body of the snare device and is separately coupled by a conductor to a high frequency generator. In this arrangement, the ring or surface electrode at the distal tip of the tubular body forms one electrode while the snare comprises the second electrode. Again, by looping the snare about the polyp and then retracting the loop into the distal end of the tubular body, the stem of the polyp is made to bridge the two electrodes to severe the polyp. By proper application of the high frequency current as the snare is being drawn about the stalk of the polyp, cauterization of the wound is accomplished.
The present invention differs from the prior art as represented by the Treat and Komiya patents discussed above in that it is designed for monopolar operation. In a monopolar device, rather than positioning two electrodes in close proximity to one another and applying a voltage between them, a large area body plate is made to intimately engage the leg or buttocks of the patient and it serves as the return electrode. The active electrode is affixed to the surgical instrument and is connected to the electrosurgical generator. In designing prior art monopolar polypectomy snares, the only active electrode on the instrument has been the loop projecting from the distal end of the instrument's tubular body. Thus, a physician could cut with the loop, but its ability to coagulate at the same time has been marginal, at best. A surgeon using the monopolar instrument would be required to do an instrument exchange in the endoscope once the polyp is severed in order to provide a separate instrument for coagulating the tissue and effecting hemostasis. The delay in making the instrument switch will often result in sufficient bleeding and obscuring of the optical system of the endoscope, thereby requiring further steps of irrigating and aspirating the surgical site to effectively clean off the endoscope optics.
It is the primary object of the present invention to provide a monopolar snare type electrosurgical instrument which also embodies a monopolar electrode for coagulating tissue by electrodesiccation.